Large capacitors with high capacitance values require large chip area, and hence result in difficulty in the formation of integrated circuits. Conventional capacitors include planar-type capacitors and trench-type MOS capacitors. The capacitor plates of the planar-type capacitors are parallel to the major surfaces of the respective substrate. The process for forming the planar-type capacitors is simple. However, planar-type capacitors also require large areas.
On the other hand, trench-type MOS capacitors comprise vertical portions perpendicular to the major surface of the respective substrates, and extending into the respective substrates, and hence the required chip areas are reduced. However, the process for forming the trench-type MOS capacitors is complicated.